1. Field of the Invention
The invention relates to the metallurgy of non-ferrous metals, and in particular, to the electrolytic production of magnesium in a continuous process line.
2. Description of the Prior Art
Metallic magnesium is produced by passing direct electric current between anodes and cathodes suspended in facing spaced relation in a molten salt bath containing magnesium chloride, within an enclosed cell chamber. The electrolysis of magnesium chloride in the bath, causes molten magnesium metal to be released at the cathode surfaces while chlorine gas is generated at the anode surfaces. The metal, being lighter than the bath, rises along the cathode surfaces, while the gas rises through the bath in a plume of bubbles from each anode surface to collect in a gas space within a working space above the level of the bath. A solid or semi-solid chlorine-magnesium raw material is utilized in the production of magnesium in the continuous production lines. This raw material is loaded either into a process area of an electrolytic cell or into a special melting device forming a part of the continuous production line. It is typically recommended to load the solid chlorine-magnesium raw material at a surface of a bath in the electrolysis compartment of the cell.
An example of an apparatus for electrolytic production of magnesium is provided by U.S. Pat. No. 4,308,116. The electrolytic cell disclosed by the patent contains a special section adapted for receiving and melting a solid magnesium chloride. An upwardly extending gas exhaust bell is formed for evacuation of gases from the electrolysis section. The bell includes a feeding pipe for loading a solid raw material.
A cross-wall extends transversely in the electrolysis compartment. It separates the cathodes in the electrolysis compartment, restricts the treatment time of the non-molten material in the electrolytic section and contributes to the discharging thereof into the metal collecting chamber. In the metal collecting chamber, the non-molten raw material is mixed with the molten metal, resulting in an undesirable solidification of the former. Another important drawback of this patent is that the loading of solid material takes place in the vicinity of the cross-wall. The losses are especially increased when solid carnallite is utilized as a raw material. This is because the required volume of the loaded material per unit of the electrical current intensity is doubled in this case, compared to the loading of magnesium chloride.
Furthermore, loading of a free flowing solid or semisolid raw material into the area adapted for evacuation of the anode gasses leads to contamination of the gasses by fine particles or of the raw material dust.
Another example of the electrolytic cell according to the prior art is illustrated in FIG. 1. A section for loading and melting of a solid raw material is formed between two supporting anodes 13. After loading of the raw material, as illustrated by the arrows, the flow of chlorine gas contaminated by a dust moves directly to a rear wall 29 and a gas discharging outlets 17. A short distance between the loading area and the gas discharging outlets does not provide enough space for efficient separation of the chlorine gas from the dust particles of the raw material. Thus, the degree of contamination of the aspirated gases within the gas evacuation system is high. Therefore, further utilization of the anode gases in this prior art arrangement requires additional steps of cleaning, which ultimately increases operational costs of the system.
One aspect of the invention provides an apparatus for electrolytic production of magnesium including at least one electrolysis compartment and at least one metal collecting compartment separated from each other by a partition wall. A plurality of upright anode elements is interspread with a plurality of cathode elements within the electrolysis compartment. The electrolysis compartment is formed with at least one section for receiving and melting of a substantially solid raw material. Each section is defined between two adjacent receiving anodes and has an elongated loading inlet for directing of the substantially solid raw material. At least one gas discharging outlet is provided for discharging of chlorine gas developed at the plurality of anodes. A baffle is supported by the receiving anodes at ends thereof remote from the partition wall and in the vicinity of the gas discharging outlet. The baffle prevents direct flow of a mixture of chlorine gas and a dust resulted from loading of the substantially solid raw material into the gas discharging outlet. The baffle diverts the flow away from the gas discharging outlet and toward the partition wall prior to entering the gas discharging outlet.
As to another aspect of the invention, a gap is formed between an end of each receiving anode and the partition wall, so that the mixture before entering the gas discharging outlet passes through gaps between the receiving anodes and the partition wall substantially extending the route of the flow of the mixture and enhancing separation of the chlorine gas from the dust.
As to a further aspect of the invention, the baffle is formed with top, bottom and side portions. The top portion engages an upper closure of the electrolysis compartment, the side portions are supported by the receiving anodes and the bottom portion is submerged into the electrolyte.
According to still another aspect of the invention, spaces between two receiving adjacent anodes in each loading and melting section are greater than the spaces between the remaining adjacent electrodes in the electrolysis compartment. Each loading and melting section further includes at least two cathodes positioned between the receiving anodes and spaced from each other at a distance substantially equal to 2-3 average spaces between the remaining adjacent electrodes in the electrolysis compartment. The height of the cathodes in the loading and melting section is about 1.05-1.015 of the remaining cathodes in the electrolysis compartment.
According to a still further aspect of the invention, the elongated loading inlet is in the form of a pipe-shaped member which is spaced from the rear ends of the anodes in the electrolysis compartment at a distance substantially equal to 0.25-0.33 of the width of the anodes. Each metal collecting compartment is formed with at least one internal cover facing the direction of electrolyte and at least one external cover. The gas aspiration from the area under the internal cover is connected to a system of gas evacuation from the electrolysis compartment. A system of sanitary gas evacuation is located between the external and internal covers.
The present invention causes increase of the service life of the electrolytic cell which utilizes a solid raw material and reduces the cost of magnesium production. This is due to the increased durability of its structural elements. The lower portion of the curtain or the dividing partition is made of molten-cast materials, such as for example, korvishite. The upper portion of the partition is formed from materials of mullite type or refractory concrete. These materials are less sensitive to heat changes. Korvishite is more resistant to the melts containing impurities of hydrogen chloride.